1. Technical Field
The present invention relates to equipment and methods used in subterranean wells, and more particularly to a tie back seal and tie back seal receptacle assembly and method.
2. Background Art
Wellbores are typically formed by drilling and thereafter lining a borehole with steel pipe called casing. The casing provides support to the wellbore and facilitates the isolation of certain areas of the wellbore adjacent hydrocarbon bearing formations. The casing typically extends down the wellbore from the surface of the well and the annular area between the outside of the casing and the borehole in the earth is filled with cement to permanently set the casing in the wellbore.
As the wellbore is drilled to a new depth, additional strings of pipe are run into the well to that depth whereby the upper portion of the string of pipe, or liner, is overlapping the lower portion of the casing. The liner string is then fixed or hung in the wellbore, usually by some mechanical means such as a setting sleeve hanger, expandable hanger, or other means well known in the art.
In some instances wells are completed with the remote perforating of liner to provide a fluid path for hydrocarbons to enter the wellbore where they flow into a screened portion of another smaller tubular or production tubing. In these instances, the wellbore around the tubing is isolated with packers to close the annular area and urge the hydrocarbons into the production tubing. In other completions, the last string of liner extending into the wellbore is itself pre-slotted or perforated to receive and carry hydrocarbons upwards in the wellbore. In these instances, production tubing is usually connected to the top of the liner to serve as a conduit to the surface of the well. In this manner, the liner is “tied back” to the surface of the well.
In order to complete these types of wells, the production tubing is inserted in the top of a liner in a sealing relationship usually accomplished by utilization of a polished bore receptacle in the liner top. A polish bore receptacle has a smooth cylindrical inner bore designed to receive and seal a tubular having a seal assembly on its lower end. The polished bore receptacle and seal assembly combination allows the production tubing to be “stung” into the liner in a sealing relationship and be selectively removed therefrom. As herein, the term “polished bore receptacle” refers to a device used to locate and seal a first tubular in a second tubular. The term “smooth bore receptacle” is also used in the industry. For disclosure regarding tie back receptacles and tie back seal mandrels consider the following U.S. Patents and U.S. Patent Application Publications, each of which are incorporated herein by reference for all purposes: 2009/0200041, A1, to Watson, filed Feb. 7, 2008; 2006/0269360, to Rowley, published November, 2006; 2005/0217866, to Watson, published October 2005; 2006/0065403, to Watson, published March 2006;, U.S. Pat. No. 7,195,073, to Fraser, filed May 1, 2003;, U.S. Pat. No. 7,854,266, to Watson; U.S. Pat. No. 7,779,910, issued Aug. 24, 2010, to Watson; U.S. Pat. No. 6,056,061, to Ross. For further disclosure, see SPE 106757, Expandable Liner Hanger Resolves Sealing Problems and Improves Integrity in Liner Completion Scenarios, James Willford and Pete Smith (2007), which is incorporated herein by reference for all purposes.
Mechanical mechanisms, such as latches, are also used in the industry to hold tie back seal mandrels in position in relation to tie back receptacles. For example, commercial latches are available from Halliburton Energy Services, Inc., under the trade names Ratch Latch and Versalatch.
One common type of tie back assembly is a mono-diameter tie back assembly. The typical mono-diameter tie back receptacle (TBR) and seal mandrel for a liner generally have a pressure rating about half the liner pressure rating because geometric limitations require the TBR and the seal mandrel to each be approximately half the liner thickness. The assembly has a relatively low pressure rating, which limits the use of the tie back assembly and makes it unworkable in some wells.
Consequently, there exists a need for a tie back assembly with an increased pressure rating for the tie back seal and the TBR. Improvement of the pressure rating should allow use of such tie back assemblies in, for example, deep water wells. Deep water wells require higher pressure ratings for liners. Further, new government and industry regulations may require higher pressure ratings. The disclosed invention has higher pressure ratings than prior art assemblies.